Two consecutive generations of mice were raised at graded room temperatures ranging from 12 to 32°C at intervals of 2°C. The delivery rate decreased at 30 and 32°C, and the litter size and weaning rate decreased above 28°C. No significant difference was demonstrated within the 12-26°C range for any reproduction parameters observed. The body weights of the first-generation mice born at 22°C and transferred to rooms at assigned temperature did not significantly differ within the 14-28°C range after 8 and 16 weeks of exposure. The second-generation mice born and reared at various temperature levels did not show significant inter-group difference in weight within the 20-26°C range at any age in the growth period. No significant inter-group difference was observed within the 20-26°C range in respect of food and water intakes in the second-generation mice. Hematological values and organ weights in the first and second generation mice of both sexes did not significantly differ in any parameter within the 20-26°C range. The results suggest the temperature range of 20-26°C to be optimal for laboratory mouse rooms.